The previous method of dissociating metal dihalides for the purpose of achieving laser action was by means of ultraviolet photons supplied from another laser employed as an excitation pump. Because of the limited efficiency of the pump laser, which was typically less than one percent, the overall efficiency of achieving lasing by photodissociation in metal halides is thus inherently limited as was explained in a publication by Erhard J. Schimitschek, John E. Celto and John Trias which appeared in "Applied Physics Letters" 31, at page 608, Nov. 1, 1977.
In that article it was noted that laser action achieved by photodissociation of HgBr.sub.2 in the vapor phase employed excitation pump radiation produced by an ArF excimer laser generating a 193 nm wavelength output. In transverse photo excitation, laser energy of wavelengths from 502 nm to 505 nm were produced by the HgBr laser, the measured output energy being 0.25 mJ at a pump energy level of 7 mJ. Therefore, assuming an approximated one percent efficiency of the ArF excimer laser used as an excitation pump, it can be readily appreciated that the overall efficiency of such photodissociation is severely inherently limited. Accordingly, comparable laser action achieved with metal dihalides which does not require optical pumping from a secondary excitation laser is highly desirable because of its potential for operating at much improved levels of efficiency overall.
Somewhat improved performance has evolved by the use of a nitrogen-helium buffer gas. An article covering N.sub.2 -He gases and entitled "Discharge pumped mercuric halide dissociation lasers" by R. Burnham appeared in the July 1978 issue of Applied Physics Letters, Vol. 33, No. 2. However, laser outputs and laser efficiencies are still not as high as anticipated. The dissociation process appears to need a buffer gas that will enhance the lasing phenomena by providing vibrational relaxation time at the B and X states and aiding discharge uniformity and by participating in the dissociative excitation process.